Cool and breezy Friday; showers over weekend

It should be a rather cool breezy day with high temperatures in the upper 60s, a refreshing change after weeks of unseasonable warm weather. You might even need a sweater.

But it won't last long. Warmer conditions should return over the weekend, along with a good chance of showers.

South Florida's Friday forecast calls for partly sunny skies with afternoon highs in the upper 60s, overnight lows in the upper 50s and low 60s and wind gusts up to 31 mph.

Temperatures should rebound back to the upper 70s on Saturday and the low 80s on Sunday. There is a 40 percent chance of rain both days.

Another cold front should lower temperatures into the upper 50s on Monday night and Tuesday morning.

Central Florida's Friday forecast: Mostly sunny and breezy with highs in the upper 50s and lows in the mid 40s. The weekend should be considerably warmer.

Cold North Florida: Temperatures were expected to plummet into the upper 20s by this morning in Tallahassee.

Jet stream: From weather expert Jim Lushine:

What does the temperature difference between Grand Forks, N.D., and Fort Lauderdale have to do with how long it takes to fly between West Palm Beach and Dallas?

It all relates directly to the speed of the jet stream.

The jet stream is a river of high-speed air, which in the winter is located at an altitude of five to seven miles above the ground, near the level where jet aircraft operate, and hence its name.

With a sufficiently large temperature difference across the country, winds in the jet stream can exceed 200 mph. This will have a pronounced effect on the time that it takes for jet aircraft to fly across the country, depending on which direction the flight is headed.

Flying from West Palm Beach to Dallas against a head wind can add 15 to 20 minutes tor more to the length of a flight while a flight in the opposite direction can be at least 15 to 20 minutes shorter.